1. Field of the Invention
The present invention relates to a fuel injection valve and a means for reducing the surge pressure occurrence or propagation in the fuel injection valve of the accumulator injection system (a common-rail injection system), the fuel injection valve injecting the high pressure fuel supplied from a pressurized fuel accumulator, into an engine combustion chamber, through at least one nozzle hole provided in a nozzle of the valve.
2. Background of the Invention
FIG. 5 shows an outline cross-section as to an example of a fuel injection valve of the accumulator injection system (a common-rail injection system). As shown in FIG. 5, the fuel injection valve 100 comprises: a nozzle 1 that is provided with at least one nozzle hole 4 which are placed at the tip part of the nozzle, thereby fuel is injected through the nozzle hole, and
a nozzle needle (valve) 2 is fitted into the inner cylindrical space of the nozzle 1 so that the nozzle needle 2 slides in the inner cylindrical space with reciprocating movements; a spacer 6; and, a (fuel injection valve) body 7 to which the nozzle 1 and the spacer 6 are tightly attached by a nozzle holder 17, for example, by the screw mechanism of the nozzle holder.
While the nozzle needle 2 is being pressed on a valve seat 5a of the nozzle 1, the fuel injection valve is kept under a closed condition. The nozzle needle 2 is annexed to a needle spring shoe 8a above the nozzle needle 2 and a push rod 8b that is placed above the a needle spring shoe 8a and fitted into the inner cylindrical space of the fuel injection valve body 7 so that the push rod slides in the inner cylindrical space with reciprocating movements. The numeral 9 denotes a needle spring that presses the nozzle needle 2 against the valve seat 5a, namely, the needle spring determines the opening pressure of the nozzle needle valve.
The numeral 11 denotes a fuel inlet piece in which a fuel inlet passage 12 is formed. The fuel inlet passage 12 communicates with a fuel passage 14a and a fuel passage 14b that are formed in the fuel injection valve body 7, thereby the fuel passage 14a communicates with a fuel sump 5 that is a space filled with fuel in the nozzle and surrounds the nozzle needle 2.
On the other hand, the fuel passage 14b communicates with a backward space of the push rod 8b, namely, a space above the push rod 8b via an orifice 13; thus, with a fuel pressure in the backward space, the push rod 8b, the needle spring shoe 8a and the nozzle needle can be thrust downward toward the valve seat (in the case where the needle valve is closed).
The numeral 14 denotes a solenoid that actuates a pilot needle valve locating at an upper side of the fuel injection valve; when the pilot needle valve is closed, the pressure in the space above the push rod holds so that the nozzle needle 2 is closed; on the other hand, when the pilot needle valve is opened, the pressure in the space above the push rod is released so that the nozzle needle 2 is opened. Thus, the fuel injection timing is controlled. In addition, the numeral 24 denotes a fuel drain passage.
In the fuel injection valve 100 as described above, when the solenoid 14 activates the pilot needle valve, a passage 10 is opened; at the same time, the fuel from the fuel inlet passage 12 is supplied toward the fuel sump 5 through the fuel passage 14a; then, the fuel pressure force acts on the nozzle needle 2 from the lower side thereof; thus, the nozzle needle comes apart from the valve seat 5a, and the fuel is injected into the combustion chamber through the nozzle hole 4.
Further, the patent reference 1 (JP2000-27734) discloses an example as to the fuel injection valve of the accumulator injection system, whereby the steep rising of the fuel injection rate is restrained so as to reduce the nitrogen oxide generation (NOx generation).
FIGS. 6, 6(A), 6(B) and 6(C) explain the state of the fuel injection as to the fuel injection valve 100 of the accumulator injection system (i.e. a common-rail injection system) as depicted in FIG. 5.
In FIG. 6, when the fuel injection valve 100 of the accumulator injection system (i.e. the common-rail injection system) is about to stop an injection shot, a high pressure fuel injection rate (see FIG. 6(C)) is maintained until the moment before the injection shot is completed in order to inject the highly pressurized fuel that is accumulated in the common-rail; under such a condition, the nozzle needle 2 is going to sit on the valve seat 5a so that the fuel injection valve closes. In this connection, FIG. 4(A) depicts the change as to the lift of the nozzle needle 2.
As explained above, the change of the fuel injection rate during the nozzle needle closing is so great that a high surge pressure S is caused in the high-pressure fuel lines (such as a high-pressure line 19, the fuel passage 14a and the fuel passage 14b) as depicted in FIG. 4(B).
The larger the capacity of the fuel injection valve, the more remarkable the surge pressure S. When the level of the surge pressure S exceeds an allowable limit, the fuel injection performance is spoiled and the strength of the components of the injection valves is impaired.